diff --git a/libc/arch-x86/string/strcat.S b/libc/arch-x86/string/strcat.S
new file mode 100644
index 0000000..c75f38a
--- /dev/null
+++ b/libc/arch-x86/string/strcat.S
@@ -0,0 +1,74 @@
+/*	$OpenBSD: strcat.S,v 1.8 2005/08/07 11:30:38 espie Exp $ */
+/*
+ * Written by J.T. Conklin <jtc@netbsd.org>.
+ * Public domain.
+ */
+
+#include <machine/asm.h>
+
+#if defined(APIWARN)
+#APP
+	.section .gnu.warning.strcat
+	.ascii "warning: strcat() is almost always misused, please use strlcat()"
+#NO_APP
+#endif
+
+/*
+ * NOTE: I've unrolled the loop eight times: large enough to make a
+ * significant difference, and small enough not to totally trash the
+ * cache.
+ */
+
+ENTRY(strcat)
+	pushl	%edi			/* save edi */
+	movl	8(%esp),%edi		/* dst address */
+	movl	12(%esp),%edx		/* src address */
+	pushl	%edi			/* push destination address */
+
+	cld				/* set search forward */
+	xorl	%eax,%eax		/* set search for null terminator */
+	movl	$-1,%ecx		/* set search for lots of characters */
+	repne				/* search! */
+	scasb
+
+	leal	-1(%edi),%ecx		/* correct dst address */
+
+	.align 2,0x90
+L1:	movb	(%edx),%al		/* unroll loop, but not too much */
+	movb	%al,(%ecx)
+	testb	%al,%al
+	jz	L2
+	movb	1(%edx),%al
+	movb	%al,1(%ecx)
+	testb	%al,%al
+	jz	L2
+	movb	2(%edx),%al
+	movb	%al,2(%ecx)
+	testb	%al,%al
+	jz	L2
+	movb	3(%edx),%al
+	movb	%al,3(%ecx)
+	testb	%al,%al
+	jz	L2
+	movb	4(%edx),%al
+	movb	%al,4(%ecx)
+	testb	%al,%al
+	jz	L2
+	movb	5(%edx),%al
+	movb	%al,5(%ecx)
+	testb	%al,%al
+	jz	L2
+	movb	6(%edx),%al
+	movb	%al,6(%ecx)
+	testb	%al,%al
+	jz	L2
+	movb	7(%edx),%al
+	movb	%al,7(%ecx)
+	addl	$8,%edx
+	addl	$8,%ecx
+	testb	%al,%al
+	jnz	L1
+L2:	popl	%eax			/* pop destination address */
+	popl	%edi			/* restore edi */
+	ret
+END(strcat)